1. Field of the Invention
The present invention relates to a device for displaying images, more particularly, to a display device employing an optical compensation film for improving visual angle and gray scale properties of the display device.
2. Description of the Related Art
Generally, a display device displays data which is obtained in the form of electric signals from a data processing unit so that a user can recognize the data. Display devices may be classified into a digital display device group and an analog display device group according to a driving method.
LCD (Liquid Crystal Display) device is one of the typical digital display devices. An LCD device has advantages such as capabilities of realizing a large-scaled screen, a high resolution, having a small size and weight, etc.
CRT (cathode ray tube) type display device is a typical analog display device. A CRT type display device has an advantage in that it facilely realizes a large-scaled screen and a high resolution at a low cost. However, the CRT type display device has disadvantages such as larger volume and heavier weight than an LCD device having the same screen size.
Hence, the LCD technology has been developed, and there is a trend of replacing CRT type display devices with LCD devices. The recent research on LCD devices has been focused on the technical development and improvement of the driving method and structure thereof. Therefore, it has been realized that LCD devices have high display quality by improving the driving method and reduced size and weight by improving the structure thereof.
In spite of the development in the driving method and structure of LCD devices, there are continuing problems such as gray scale inversion phenomenon occurring in twisted nematic (TN) LCD devices.
The gray scale inversion phenomenon means that the gray scale is inversed in an image. Generally, in an LCD device, the larger the intensity of a driving signal is, the higher its brightness is. However, in spite of the large intensity of a driving signal, there may be a portion on a display device, in which the brightness is relatively lowered. This phenomenon is called the gray scale inversion phenomenon and frequently occurs in LCD devices. The gray scale inversion phenomenon is an obstructive factor in realizing the high display quality.
Further, the gray scale inversion phenomenon causes the brightness to be lowered. This exerts a bad influence on a visual angle in which a contrast ratio is defined to 10:1 or more. As a result, the visual angle is narrowed.
Here, the fact that the visual angle is narrowed means that even if an angle formed between user""s eyes and the surface of an LCD device is slightly changed, there may be a portion in which the user cannot recognize the content of displayed information on the LCD device. This is also an obstructive factor in realizing the high display quality.
Although the gray scale inversion phenomenon may not directly affect the display operation of an LCD device, it causes the visual angle to be narrowed, thereby substantially degrading display property of the LCD device.
To solve the problem of reducing the visual angle due to the gray scale inversion phenomenon, there have been provided optical compensation films. However, the conventional optical compensating films do not solve the problem of the gray scale inversion phenomenon which is a major obstructive factor in degrading the visual angle property.
In addition, when the conventional optical compensating film is applied to a TN LCD device having improved two domains, one of the two domains is compensated but the other domain is not compensated. As a result, the TN LCD device may have a problem of xe2x80x9ctrade-offxe2x80x9d between the gray scale inversion phenomenon and the visual angle property.
It is an object of the present invention to provide an optical compensation film which is applied to a display device to prevent an occurrence of the gray scale inversion phenomenon and thus to increase the visual angle.
It is another object of the present invention to provide a method of manufacturing the optical compensating film by which an occurrence of the gray scale inversion phenomenon is prevented and the visual angle is increased.
It is another object of the present invention to provide an illuminating method in a display device using the optical compensating film by which an occurrence of the gray scale inversion phenomenon is prevented and the visual angle is increased.
It is still another object of the present invention to provide a display device in which an occurrence of the gray scale inversion phenomenon is prevented and the visual angle is increased, thereby improving the display quality.
To achieve the above and other objects of the present invention, there is provided an optical compensation film. In the optical compensation film, a first transparent member is formed on a substrate. The first transparent member has a recessed portion and a first refractive index. Light that has passed through the substrate passes through the first transparent member. A second transparent member has a protruded portion partly engaged with the recessed portion. The second transparent member has a second refractive index which is substantially the same as the first refractive index. The light passes in a first direction through an overlapped portion where the protruded portion of the second transparent member is in contact with the recessed portion of the first transparent member, and the light passes in a second direction which is different from the first direction through a non-overlapped portion in which there is a gap between the protrusion portion of the second transparent member and the first transparent member.
In anther aspect of the present invention, there is provided a method of manufacturing an optical compensation film. In the method, a first transparent member having a first refractive index is formed on a substrate. A second transparent member having a plurality protruded portions and a second refractive index, which is substantially the same as the first refractive index of the first transparent member, is aligned with the first transparent member. The protruded portions of the second transparent member are partly engaged with the first transparent member at a predetermined depth. The first transparent member is then cured.
In another aspect of the present invention, there is provided an illuminating method in a display device. Light generated from a light source is processed to form display light for displaying an image and then is supplied in a first direction. A part of the display light passes through a first position having the substantially same refractive index as that of a medium, continues to be supplied in a first direction and then reaches to user""s eyes, and the rest of the display light passes through a second position having a different refractive index than the medium, continues to be supplied in a second direction different from the first direction and then reaches to the user""s eyes.
In another aspect of the present invention, there is provided an LCD device. In the LCD device, an LCD panel assembly has an LCD panel in which a liquid crystal layer is sandwiched between two transparent substrates for controlling electric field therebetween in a unit of a minute surface area. The transmissivity of the liquid crystal layer is changed depending on intensity of the electric field. An optical path changing film has a first transparent member and a second transparent member. The first transparent member is disposed on the LCD panel with a recessed portion. The first transparent member has a first refractive index, and light that has passed through the substrate passes through the first transparent member. The second transparent member has a protruded portion partly engaged with the recessed portion of the first transparent member. The second transparent member has a second refractive index which is substantially the same as the first refractive index. A backlight assembly provides light to the liquid crystal layer. The light advances in a first direction at an overlapped portion in which the protruded portion is in contact with the recessed portion, and advances in a second direction that is different from the first direction at a non-overlapped portion in which there is a gap between the protruded portion of the second transparent member and the first transparent member.
According to the present invention, visual angle property of a display device is remarkably improved and the gray scale inversion phenomenon is solved using the optical compensation film, thereby improving the display property. Further, the method of manufacturing the optical compensation film is improved, thereby manufacturing a precise film for compensating the optical property with a simple method.